The search for accurate and reliable diagnostic measures has been long, and only partially successful, since significant problems remain with frequent attenuation of symptom reports. The appreciation of cognitive and communication principles associated with the process of structured diagnostic interviewing has lead to renewed efforts to understand the determinants of unreliability and reduce the phenomenon of diagnostic and symptomatic attenuation. This study will systematically examine the nature, sources and correlates of unreliability in repeated measurements of child psychopathology using the Present State Version of the NIMH- DISC. It will investigate the impact of two experimental modifications on the test-retest reliability of the DISC. The sample will be derived from the general population and balanced with regards to age and probable diagnosis of child. Following initial enumeration and recruitment of eligible households via telephone, a brief screen will be given to both the adolescent (aged 9-16) and a parental informant. Screen positives, derived independently from both informants and a proportion of the screen negatives will then be invited to participate in a second stage procedure. This will include a test- retest reliability study of the NIMH-DISC (Present State Version) examining the effect of two modifications to the DISC intended to reduce symptomatic and diagnostic attenuation. A factorial design will enable the impact of a series of graphical aids to symptom recall, as well as the effect of providing a cognitive road map to the interview and allowing subject to choose the order in which diagnostic modules are completed, to be measured. Addition of a detailed discrepancy interview protocol/cognitive interview and associated measurements of factors predictive of unreliability will also enable examination of the determinants of unreliability and a more qualitative assessment of the effects of the experimental interventions.